CALCULATION OF THE P-T PHASE-DIAGRAM OF ZR IN DIFFERENT APPROXIMATIONS FOR THE EXCHANGE-CORRELATION ENERGY

The full-potential linear muffin-tin orbital method is used within the local density approximation and generalized gradient approximation (G GA) to calculate the total energy and equilibrium lattice properties f or the observed phases of Zr. The temperature dependences of the free energy, specific volume, bulk modulus, Debye temperature, and Gruneise n constant are found for these structures within the Debye model. For most quantities, a good quantitative agreement with experiment is obta ined. The P-T phase diagram constructed from the calculated thermodyna mical Gibbs potentials within the GGA fits well the available room-tem perature data on the alpha-->omega and omega-->beta transitions. At am bient pressure, we get Tbeta-->alpha = 1193 K, which is close to the o bserved value.